摘要:

Anomalous electrostatic dissipation in a collisionless plasma is caused by an induced charge separation which, in the homogeneous case, is particularly large when high local concentrations of the two species occur close together. If a turbulent plasma state has evolved from an unstable initial state which is only slightly perturbed, particle bunching (with maximum number density proportional toT0−1/4at low initial temperatureT0) takes place at points of overtaking ‐ reversal of the ordering of particles with the same initial velocity. Overtaking is governed by a differential equation which involves the applied field only implicitly. Use of this equation in a simple case shows that a bunch of particles of one species causes bunching in the other species, and that the sense of the resulting turbulent electric field is such as to oppose the laminar motion. The characteristic time of formation of an ion bunch by an electron bunch of incremental number density&Dgr;nis(4&pgr;e2&Dgr;n/mi)−1/2. When the charge separation is expressed in terms of Lagrangian coordinates, a possible example of this phenomenon is revealed by the appearance of islands in the relevant curve. The islands represent adjacent bunches of electrons and ions, and preliminary investigation indicates that they might provide a major portion of the dissipation. A computer study to amplify these findings is proposed.

ISSN:0031-9171    

DOI:10.1063/1.1694400

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Projection operator techniques have been applied to derive a coupled set of exact kinetic equations describing microscopic density fluctuations in an infinite, fully‐ionized, classical plasma in thermal equilibrium. The time dependence of the nonlocal collision terms in these equations is then approximated in such a way as to yield the correct short and long time behavior of density fluctuations, while allowing the explicit calculation of the dynamic structure factorS (k ,&ohgr;)characterizing electron density fluctuations in classical plasmas of arbitrary density. This theory is then applied to analyze light scattering from dense, collision‐dominated plasmas, and the results of these calculations are found to compare favorably with both experimental data as well as with earlier theories (at least in the regimes in which these earlier theories are valid).

ISSN:0031-9171    

DOI:10.1063/1.1694401

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The nonlinear evolution of the decay instability in a plasma driven by an externally imposed pump field oscillating near the electron plasma frequency is considered. For a plasma with comparable electron and ion temperatures and for weak pump fields, nonlinear Landau damping of electron plasma waves on the ions is the dominant nonlinearity. It is demonstrated that a one‐dimensional wave kinetic equation describes the dominant interactions for spectral intensities whose characteristic angular width is small. This equation is solved numerically with the exact form for the matrix element which describes the coupling. An analytical solution is found for the spectral intensity in the limit in which the (small) spontaneous emission term is neglected. The plasma wave energies obtained both numerically and analytically are in good agreement. General characteristics of the plasma wave spectrum agree with observations in the ionosphere. The enhanced dissipation rate of the pump due to the presence of the fluctuations agrees with that observed in a laboratory experiment.

ISSN:0031-9171    

DOI:10.1063/1.1694402

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Bremsstrahlung measurements have been used to determine the axial distribution of density and temperature in an electron cyclotron heating experiment. The results show two heating mechanisms. Low energy electrons turn at the resonance position and are resonantly heated. High energy electrons turn well inside their resonance position and are nonresonantly heated.

ISSN:0031-9171    

DOI:10.1063/1.1694403

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The stabilizing effects that a beam of longitudinally nonuniform density imposes on beam‐plasma instabilities are investigated using a hydrodynamic model adapted for an infinite, one‐dimensional beam‐plasma system. The electron beam is characterized by either of two types of longitudinal inhomogeneity—square‐wave or sinusoidal. The results, for the square‐wave type of inhomogeneity, indicate a disappearance of the convective instabilities below a threshold frequency as well as a reduction in the growth rate for the remainder of the spectrum. Similar results are obtained for the case of a high‐frequency sinusoidal pulsation of the beam density. Effects resulting from finite temperature plasma electrons are also discussed.

ISSN:0031-9171    

DOI:10.1063/1.1694404

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A remote feedback technique has been employed to stabilize an ion‐acoustic type of instability in a plasma with a low frequency density modulation. The plasma is unstable for certain values ofnanddn/drwhich occur during part of the period of the low frequency modulation. Agreement with the Van der Pol approach is good when the instability is allowed to saturate and the cross field diffusion is shown to decrease when the plasma is stabilized.

ISSN:0031-9171    

DOI:10.1063/1.1694405

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A numerical solution of the Boltzmann‐Krook equation for the thermal creep of a rarefied gas in a circular tube is compared with Knudsen's transpiration formula, Maxwell's equation, and the model of Bosanquet.

ISSN:0031-9171    

DOI:10.1063/1.1694406

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

An analysis is presented for the magnetohydrodynamic flow due to a constant mass source expanding into a uniform magnetic field. The shape of the free surface is calculated as a function of time.

ISSN:0031-9171    

DOI:10.1063/1.1694407

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A probe excites two waves, a slow and a fast wave in a hot magnetized plasma when&ohgr;<&ohgr;pand&ohgr;c≫&ohgr;p. These waves propagate only within a cone of half‐cone anglesin−1(&ohgr;/&ohgr;p). It is found that the sheath around the probe effectively attenuates the two waves and the slow wave is attenuated more than the fast one.

ISSN:0031-9171    

DOI:10.1063/1.1694408

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A spherical probe is subjected to a potential ramp with rise time of the order of the electron diffusion time, after which, the final potential is maintained constant. The electron current overshoots its final value by an amount proportional to the electron conductivity.

ISSN:0031-9171    

DOI:10.1063/1.1694409

出版商:AIP    

年代:1973

数据来源: AIP